The use of progressive resistance exercises for therapeutic and rehabilitative purposes and the use of progressive resistance exercises involving heavy weights for marked increases in strength and endurance were developed and employed during World War II. Since that time the use of progressive increases in weight has grown widely in popularity.
Exercising muscles against progressively increasing weights not only results in added strength and endurance in the muscles, but also in the improvement of neuromuscular coordination and in a more efficient functioning of the cardiovascular and respiratory systems.
Apparatus such as dumbells and barbells have long been used for progressive resistance exercises, but have the shortcomings of sometimes causing strains and hazards, and presenting balancing problems.
Certain multistation exercise machines have also been used for progressive resistance exercises, but they usually require too much floor space and are relatively complex and too expensive to manufacture as a result.
A single-station exercise machine has been developed in order to overcome many of the disadvantages of the multi-station kind (see U.S. Pat. No. 3,635,472 for example), but the machine is still more complex, bulky, weighty and costly to produce because of the necessity of cables, pulleys, etc.